1

Objectives
● Explain and analyze the operation of both half and full wave rectifiers
● Explain and analyze filters and regulators and their characteristics
● Explain and analyze the operation of diode limiting and clamping circuits
● Explain and analyze the operation of diode voltage multipliers
● Interpret and use a diode data sheet
● Troubleshoot simple diode circuits
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Load-Line Analysis
The load line plots all possible combinations of diode current ( I
D
) and voltage ( V
D
) for a given circuit.
The maximum I
D equals E/R , and the maximum V
D equals E .
The point where the load line and the characteristic curve intersect is the Q-point, which identifies I
D and
V
D for a particular diode in a given circuit.
3

Series Diode Configurations
Forward Bias
Constants
•
Silicon Diode: V
D
= 0.7 V
•
Germanium Diode: V
D
= 0.3 V
Analysis (for silicon)
• V
D
= 0.7 V (or V
D
= E if E < 0.7 V)
•
V
R
= E – V
D
•
I
D
= I
R
= I
T
= V
R
/ R
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Series Diode Configurations
Reverse Bias
Diodes ideally behave as open circuits
Analysis
• V
D
= E
•
V
R
= 0 V
• I
D
= 0 A
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Parallel Configurations
V

0.7 V
D
V

V

V

0.7 V
D1 D2 O
V

9.3 V
R
I
R

E

V
D 
R
10 V

.7 V
.33kΩ

28 mA
I

I

D1 D2
28 mA
2

14mA
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Half-Wave Rectification
The diode only conducts when it is forward biased, therefore only half of the AC cycle passes through the diode to the output.
The DC output voltage is 0.318
V m
, where V m
= the peak AC voltage .
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PIV (PRV)
Because the diode is only forward biased for one-half of the AC cycle, it is also reverse biased for one-half cycle.
It is important that the reverse breakdown voltage rating of the diode be high enough to withstand the peak, reverse-biasing AC voltage.
PIV (or PRV) > V m
• PIV = Peak inverse voltage
•
PRV = Peak reverse voltage
• V m
= Peak AC voltage
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Full-Wave Rectification
The rectification process can be improved by using a full-wave rectifier circuit.
Full-wave rectification produces a greater DC output:
•
Half-wave: V dc
= 0.318
V m
•
Full-wave: V dc
= 0.636
V m
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Full-Wave Rectification
Bridge Rectifier
•
Four diodes are connected in a bridge configuration
• V
DC
= 0.636
V m
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Full-Wave Rectification
Center-Tapped Transformer
Rectifier
Requires
•
Two diodes
•
Center-tapped transformer
V
DC
= 0.636
V m
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Summary of Rectifier Circuits
Rectifier
Half Wave Rectifier
Bridge Rectifier
Ideal V
DC
V
DC
= 0.318
V m
Realistic V
DC
V
DC
= 0.318
V m
– 0.7
V
DC
= 0.636
V m
V
DC
= 0.636
V m
– 2(0.7 V)
Center-Tapped Transformer
Rectifier V
DC
= 0.636
V m
V
DC
= 0.636
V m
– 0.7 V
V m
= peak of the AC voltage.
In the center tapped transformer rectifier circuit, the peak AC voltage is the transformer secondary voltage to the tap.
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Diode Clippers
•
The diode in a series clipper
“clips” any voltage that does not forward bias it:
•
A reverse-biasing polarity
• A forward-biasing polarity less than
0.7 V (for a silicon diode)
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Biased Clippers
Adding a DC source in series with the clipping diode changes the effective forward bias of the diode.
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Parallel Clippers
The diode in a parallel clipper circuit “clips” any voltage that forward bias it.
DC biasing can be added in series with the diode to change the clipping level.
15

Summary of Clipper Circuits
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Summary of Clipper Circuits
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Clampers
A diode and capacitor can be combined to “clamp” an AC signal to a specific DC level.
18

Biased Clamper Circuits
The input signal can be any type of waveform such as sine, square, and triangle waves.
The DC source lets you adjust the DC camping level.
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Summary of Clamper Circuits
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Voltage-Multiplier Circuits
Voltage multiplier circuits use a combination of diodes and capacitors to step up the output voltage of rectifier circuits .
• Voltage Doubler
•
Voltage Tripler
• Voltage Quadrupler
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Voltage Doubler
This half-wave voltage doubler’s output can be calculated by:
V out
= V
C2
= 2V m where V m
= peak secondary voltage of the transformer
22

Voltage Doubler
•
Positive Half-Cycle o D
1 conducts o D
2 is switched off o Capacitor C
1 charges to V m
•
Negative Half-Cycle o D
1 is switched off o D
2 conducts o Capacitor C
2 charges to V m
V out
= V
C2
= 2V m
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Voltage Tripler and Quadrupler
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Practical Applications
• Rectifier Circuits
– Conversions of AC to DC for DC operated circuits
–
Battery Charging Circuits
• Simple Diode Circuits
–
Protective Circuits against
– Overcurrent
–
Polarity Reversal
–
Currents caused by an inductive kick in a relay circuit
• Zener Circuits
– Overvoltage Protection
–
Setting Reference Voltages
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